The present invention relates generally to a retractable rear bumper means for attachment to the rear of self-propelled dump trucks and the like, particularly those dump trucks having boxes which overhang the rear axles and extend rearwardly thereof. These structures provide a hazard for rear-end collisions, particularly those in which the impact is moderate, and wherein the occupants of the rear vehicle involved in the rear-end collision are exposed to impact with the base of the box of the dump truck. In particular, rear-end collisions of this type expose the occupants of the oncoming rear vehicle to extremely hazardous conditions, since the oncoming vehicle frequently will find no significant abutment surface until the forward portion of the oncoming vehicle strikes the axle housing or rear wheels of the dump truck.
In the regulation of safety devices for self-propelled vehicles such as trucks and the like, means are frequently provided for having bumper bars disposed at the rear of a truck or other vehicle in order to protect occupants of vehicles which may become involved in rear-end collisions with the truck. Specifically, trucks which have conventional boxes do not present significant problems, inasmuch as the box is not raised or lowered during the normal operation of the vehicle. However, dump trucks present an unusual and exceptional problem inasmuch as the boxes of the dump truck are routinely raised and lowered during operation of the vehicle, and safety regulations frequently exempt this type of vehicle from the rear bumper requirement.
A particular problem exists in connection with self-propelled dump trucks which have boxes overhanging the rear axles of the vehicles. Such trucks are widely used in the conveying of a variety of items, but in particular in the conveying of trash and refuse. These vehicles are provided with extremely large boxes in order to accommodate the load requirements, and in order to achieve the volume necessary in the vehicle, the boxes will frequently overhang the rear axle of the supporting vehicle. When arranged in overhanging relationship, upon dumping, the rear or tailgate portion of the truck will extend or pivot downwardly toward the ground, and in doing so would bend, break, or possibly destroy any bumper means which may be disposed thereacross. On the other hand, if such a bumper bar were arranged at a position which would not interfere with the normal dumping operation, such a bar would provide little if any protection for the occupants of oncoming vehicles, since it would necessarily be disposed at a substantial elevation from the ground.
Mechanical bumper bars capable of only limited forward motion have been suggested, however such bars, unless provided with means for raising and lowering of the bumper bar would interfere with the normal use and driving of the dump truck vehicle, particularly upon backing of the vehicle in confined or crowded working areas. Accordingly, the present invention is one which permits the vehicle to be utilized with a total degree of flexibility in its operation, without adversely affecting the normal operation, and yet provides significant protection for occupants of any vehicle involved in a rear-end collision with the dump truck wherein moderate forces or impacts are present.